This application is a U.S. national stage of international application PCT/EP99/06329, filed Nov. 13, 1997.
The present invention concerns a mixture of thermoplastic and elastomeric polyolefin compositions; the mixture is partially cross-linked, and has in spite of this a good melt flow rate.
The mixtures of the present invention are particularly suitable for the production of laminated articles produced by way of the slush molding process. In particular, the mixtures are used for the production of synthetic leather to be used, for example, in the automotive industry to cover some of automobile parts.
Synthetic leathers produced from thermoplastic polyolefins are already known in the art. For example, published European patent application EP-A-633 289, on behalf of Himont Incorporated, describes the use of partially cross-linked thermoplastic and elastomeric polyolefin compositions to be used in a slush molding process for the production of synthetic leathers. Said compositions have good mechanical properties, such as high elongation at break values, therefore the laminates obtained from them are adequate for use in thermoforming processes. However, these compositions present the problem of having a low melt flow rate, and consequently a number of pinholes form in the laminates produced by slush molding.
Moreover, published European patent application EP-A-637 610, on behalf of Himont Incorporated, describes thermoplastic polyolefin compositions suitable for the production of very soft synthetic leathers using a slush molding process. The leathers produced from these compositions do not have high tensile strength and elastic recovery values.
Patent application WO 95/35344 (Reydel) also describes compositions for the production of synthetic leather by way of slush molding. These compositions comprise a heterophasic matrix made of a crystalline propylene polymer and a propylene/ethylene rubber with a small content of ethylene. In order to facilitate the removal of the leathers from the mold and prevent the surfacing of low molecular weight rubbery particles that cause problems related to sticking as well as soiling the mold, said compositions also contain a resin comprising a rubber, EPR or EPDM, either cross-linked or not cross-linked. However, in order to achieve the desired properties, such as specific levels of softness of the finished product and melt flow rate, all the compositions cited in said patent application contain extender oil, as is proven by our analyses and demonstrated in the comparative examples.
Moreover, the exemplified compositions of the above mentioned patent application WO 95/35344, according to measurements we carried out which are demonstrated in the comparative examples, present tensile strength and elongation at break values that are not completely satisfactory. Good values related to said properties are important in order to prevent lacerations of the laminate when it is being removed from the mold.